Syria’s army renewed strikes on a Kurdish district of Aleppo after fighters rejected a ceasefire meant to halt days of clashes.
At least 21 civilians were killed, and tens of thousands fled, deepening fears over Syria’s fragile transition.
The violence erupted as Damascus and Kurdish forces argued over integrating Kurdish authorities into the new government.
Authorities had announced a truce with US-backed Kurdish forces and planned their transfer to eastern regions.
Kurdish fighters refused to withdraw, saying they would defend their neighbourhoods from any assault.
The army warned residents to evacuate Sheikh Maqsud before resuming strikes on what it called military targets.
Heavy shelling echoed across the city, as the army reported soldier deaths and began combing operations.
Flights at Aleppo airport were suspended, underlining the scale of the security emergency.
Turkey welcomed the operation, while Kurdish leaders accused Damascus of abandoning dialogue.
Analysts said the clashes threaten hopes for unity in a Syria still searching for stability.